A Tectonic Shortening
The Monti Lepini are a segment of the Central Apennines, a mountain range formed by intense crustal compression. This compression was a result of the Apennine orogeny, a mountain-building event that peaked during the Miocene and Pliocene epochs (about 23 to 2.6 million years ago). The tectonic driver was the complex collision between the African and Eurasian plates, mediated by the smaller Adria microplate. As the Italian peninsula rotated counter-clockwise, it squeezed and fractured the crust, creating a fold-and-thrust belt.
The Monti Lepini consists of a thick sequence of Mesozoic-era carbonate rocks. These limestones and dolomites were originally deposited in a shallow marine environment called the Latium-Abruzzi carbonate platform from the Late Triassic to the Cretaceous period. During the orogeny, this entire platform, thousands of meters thick, was detached from its underlying basement rock. The immense pressure then sliced the platform into at least five major sheets. These sheets were shoved one on top of another in a process called thrust faulting. This stacking action pushed older, deeper rocks up and over younger, shallower ones, forming the inverted stratigraphy visible today. The total amount of horizontal compression, or crustal shortening, across this zone is estimated to be 50 kilometers.
Landscape Carved from Carbonate
The bedrock of the Monti Lepini, being predominantly limestone, is susceptible to dissolution by rainwater, a process known as karstification. This chemical weathering has sculpted the landscape above and below ground. The surface features sinkholes (dolines), dry valleys, and vast karstic plateaus where water quickly disappears underground.
Beneath the surface, an extensive network of conduits, caves, and underground rivers has formed. This subterranean drainage system makes surface water scarce, as precipitation rapidly infiltrates the fractured limestone. The groundwater flows through this hidden plumbing, eventually emerging at springs located at the base of the mountain range. These springs are a water resource for the surrounding region, with the limestone aquifers of the Monti Lepini discharging an average of 427 million cubic meters of water annually. The highest peak in the range is Monte Semprevisa, reaching an altitude of 1,536 meters (5,039 feet), a vertical profile for these geological and hydrological processes to operate.